U.S. patent application number 09/873272 was filed with the patent office on 2002-12-05 for caching signatures.
Invention is credited to Appelman, Barry.
Application Number | 20020184333 09/873272 |
Document ID | / |
Family ID | 25361310 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020184333 |
Kind Code |
A1 |
Appelman, Barry |
December 5, 2002 |
Caching signatures
Abstract
The performance of a network system having one or more requester
nodes, one or more provider nodes, and one or more intermediate
nodes is improved by determining the digital signature of a
received file, looking up the digital signature in an index of
signatures, and forwarding a previously compressed version of the
requested file when the digital signature is found in the index of
signatures.
Inventors: |
Appelman, Barry; (McLean,
VA) |
Correspondence
Address: |
ROBERT V. RACUNAS
Fish & Richardson P.C.
601 Thirteenth Street, NW
Washington
DC
20005
US
|
Family ID: |
25361310 |
Appl. No.: |
09/873272 |
Filed: |
June 5, 2001 |
Current U.S.
Class: |
709/217 ;
709/247 |
Current CPC
Class: |
Y10S 707/99931 20130101;
H04L 9/40 20220501; H04L 63/0428 20130101; H04L 63/12 20130101;
H04L 69/329 20130101; H04L 67/06 20130101; H04L 67/568 20220501;
H04L 69/04 20130101 |
Class at
Publication: |
709/217 ;
709/247 |
International
Class: |
G06F 015/16 |
Claims
What is claimed is:
1. A method for improving performance by increasing available
bandwidth in a network system that includes one or more requestor
nodes, one or more provider nodes and one or more intermediate
nodes, the method comprising: determining a digital signature of a
requested file stored by at least one provider node in the network
system; looking up the digital signature in an index of signatures;
and forwarding a previously compressed version of the requested
file that has been stored at an intermediate node when the digital
signature is found in the index of signatures.
2. The method of claim 1 further comprising compressing the
requested file and storing the digital signature in the index of
signatures when the digital signature is not found in the index of
signatures.
3. The method of claim 2 further comprising sending the compressed
version of the requested file to a requester node.
4. The method in claim 2 further comprising sending the compressed
version of the requested file to a requester node and storing the
compressed version of the requested file at the intermediate
node.
5. The method of claim 1 wherein determining the digital signature
comprises applying a hashing technique to the requested file.
6. The method of claim 5 wherein applying the hashing technique
comprises applying a version of the MD5 algorithm to the requested
file.
7. The method of claim 5 wherein applying the hashing technique
comprises applying a version of the SHA algorithm to the requested
file.
8. The method of claim 1 further comprising determining whether an
estimated time required to directly provide the requested file to a
requester node is less than an estimated time to determine if a
previously compressed version of the requested file is already
stored at the intermediate node.
9. The method of claim 2 wherein determining the digital signature
includes determining the digital signature at the provider
node.
10. The method of claim 9 wherein looking up the digital signature
includes looking up the digital signature at the provider node.
11. The method of claim 9 wherein looking up the digital signature
includes looking up the digital signature at the intermediate
node.
12. The method of claim 1 wherein determining the digital signature
includes determining the digital at the intermediate node.
13. The method of claim 12 wherein looking up the digital signature
includes looking up the digital signature at the provider node.
14. The method of claim 12 wherein looking up the digital signature
includes looking up the digital signature at the intermediate
node.
15. The method of claim 12 wherein the internediate node comprises
a caching server.
16. The method of claim 1 wherein looking up the digital signature
includes looking up the digital signature at the provider node.
17. The method of claim 1 wherein looking up the digital signature
is performed at the intermediate node.
18. The method of claim 1 further comprising receiving the index of
digital signatures from a provider node.
19. The method of claim 1 further comprising receiving the index of
digital signatures from an intermediate node.
20. The method of claim 1 wherein determining the digital signature
is performed at the provider node.
21. The method of claim 1 wherein determining the digital signature
is performed at the intermediate node.
22. An apparatus for improving the performance of a network system
by increasing available bandwidth, the apparatus being configured
to: determine a digital signature of a requested file stored by at
least one provider node in the network system; look up the digital
signature in an index of signatures; and forward a previously
compressed version of the requested file that has been stored at an
intermediate node when the digital signature is found in the index
of signatures.
23. The apparatus of claim 22 wherein the apparatus is further
configured to compress the requested file and store the digital
signature in the index of signatures when the digital signature is
not found in the index of signatures.
24. The apparatus of claim 23 further comprising an output
interface for sending the previously compressed version of the
requested file to a requester node.
25. The apparatus of claim 22 wherein the apparatus comprises a
provider node.
26. The apparatus of claim 22 wherein the apparatus comprises an
intermediate node.
27. The apparatus of claim 26 wherein the apparatus comprises a
proxy server.
28. The apparatus of claim 26 wherein the apparatus comprises an IP
tunnel.
29. The apparatus of claim 26 wherein the apparatus comprises a
caching server.
30. A computer program for increasing available storage in a
network system, the computer program being stored on a computer
readable medium and comprising instructions for: determining a
digital signature of a requested file stored by at least one
provider node in the network system; looking up the digital
signature in an index of signatures; and forwarding a previously
compressed version of the requested file that has been stored at an
intermediate node when the digital signature is found in the index
of signatures.
31. The computer program of claim 30 further comprising
instructions for compressing the requested file and storing the
digital signature in the index of signatures when the digital
signature is not found in the index of signatures.
32. The computer program of claim 31 further comprising
instructions for sending the compressed requested version of the
file to a requestor node.
33. The computer program of claim 31 wherein, the computer readable
medium comprises a requestor node.
34. The computer program of claim 31 wherein the computer readable
medium comprises a provider node.
35. The computer program of claim 31 wherein the computer readable
medium comprises an intermediate node.
36. The computer program of claim 30 wherein the computer readable
medium comprises a disc.
37. The computer program of claim 30 wherein the computer readable
medium comprises a propagated signal.
Description
[0001] This application claims priority form U.S. application Ser.
No. 08/630,846, filed Apr. 11, 1996, which is incorporated by
reference.
TECHNICAL FIELD
[0002] This invention generally relates to a computer network
system, and more particularly to managing compressed data
files.
BACKGROUND
[0003] A wide area public computer network system may include a
client computer connected to a server computer through a network
and one or more "proxy" servers. To improve performance in such a
network system, frequently requested files may be stored in a
cache, for example, so that the same files are not repeatedly
retrieved and/or transmitted across the entire expanse of a
network.
SUMMARY
[0004] In one general aspect, the performance of a network system
having one or more requestor nodes, one or more provider nodes, and
one or more intermediate nodes is improved by determining the
digital signature of a received file, looking up the digital
signature in an index of signatures, and forwarding a previously
compressed version of the requested file when the digital signature
is found in the index of signatures.
[0005] Determining the digital signature may include applying a
hashing technique to the requested file. Applying the hashing
technique may include applying a proprietary algorithm, the MD5
algorithm, the SHA algorithm, and/or some other hashing technique.
Applying the hashing technique may include using a key to decrypt
an attached signature. The requested file may include an image
file, an HTML file, a video file, an audio file, an email message,
and/or an e-mail attachment. The digital signature and/or the index
of signatures may be received from provider nodes and/or
intermediate nodes.
[0006] Implementations may include compressing the requested file
if the file's digital signature is not found in the index of
signatures and adding the file's digital signature to the index of
signatures. The compressed file may be stored locally and/or sent
to the requestor node. Implementations also may include calculating
whether providing the file directly to the requestor node is faster
than determining the file's signature and compressing the file, and
may include providing the file directly when it is faster to do
so.
[0007] The techniques may be implemented by an apparatus and/or by
a computer program stored on a computer readable medium. The
apparatus may include an intermediate node, a provider node, a web
proxy server, an IP tunnel, and/or a caching server. The computer
readable medium may include a disc, a client device, a host device
and/or a propagated signal.
[0008] The described techniques make efficient use of limited cache
storage space, which may diminish rapidly when numerous copies of
the same file are stored. Use of the digital signatures in the
manner described avoids problems associated with identical data
that can be retrieved from countless sources and referenced in many
different ways. For example, files that contain the same core data
may be identified by different file names when each file is
retrieved from a different source. Thus, use of digital signatures
avoids problems associated with having redundant data consume
valuable storage space in a cache.
[0009] Other features and advantages will be apparent from the
following description, including the drawings, and from the
claims.
DESCRIPTION OF DRAWINGS
[0010] FIG. 1 is a block diagram of a computer network system.
[0011] FIGS. 2-5 are flow charts of methods implemented by the
computer network system of FIG. 1.
DETAILED DESCRIPTION
[0012] For illustrative purposes, FIG. 1 depicts a computer network
system 100 that implements techniques for managing compressed data
files. For brevity, several elements in the figure are represented
as monolithic entities. However, these elements each may include
numerous interconnected computers and components designed to
perform a set of specified operations and/or dedicated to a
particular geographical region.
[0013] As shown in FIG. 1, the computer network system 100 includes
a requestor node 105 connected to a provider node 110 through one
or more networks 115 and one or more intermediate nodes 120. In one
implementation, the requestor node 105 is configured to send one or
more file requests to a provider node 110 through the network 115.
The provider node 110 is configured to receive and satisfy file
requests by sending requested files to the requestor node 105
through the network 115. The requestor node 105 may communicate
directly with the intermediate node 120, or the requestor node 105
may communicate directly with the provider node 110. If the
requestor node 105 is attempting to communicate directly with the
provider node 110, the intermediate node 120 may act transparently
as an intermediary between the requestor node 105 and the provider
node 110.
[0014] One example of a requestor node 105 is a general-purpose
computer (e.g., a personal computer) capable of responding to and
executing instructions in a defined manner. Other examples include
a workstation, a device (e.g., a wireless phone or a personal
digital assistant), a component, other equipment, or some
combination of these items that is capable of responding to and
executing instructions. The requestor node 105 also may include one
or more of such computers and/or devices.
[0015] The requestor node 105 may receive instructions from a
software application, a program, a piece of code, a device, a
computer, a computer system, or a combination of these elements
that independently or collectively directs operations of the node.
The instructions may be embodied permanently or temporarily in any
type of machine, component, equipment, storage medium, or
propagated signal that is capable of being delivered to the
requestor node 105.
[0016] In one implementation, the requestor node 105 includes one
or more information retrieval software applications (e.g., browser
application, e-mail application, instant messaging client, online
service provider client, interactive television client, or ISP
client) for transmitting requests to the provider node 110. The
information retrieval applications may run on a general purpose
operating system and a hardware platform that includes a general
purpose processor and specialized hardware for graphics,
communications and/or other capabilities. Another implementation
may include a wireless phone running a micro browser application on
a reduced operating system with both general purpose and
specialized hardware to operate in mobile environments.
[0017] One example of a provider node 110 is a general-purpose
computer (e.g., a server) capable of responding to and executing
instructions in a defined manner. Other examples include a personal
computer, a special-purpose computer, a workstation, a device, a
component, other equipment or some combination thereof capable of
responding to and executing instructions. The provider node 110 may
include and/or form part of an information delivery network, such
as, for example the Internet, the World Wide Web, an online service
provider, and/or any other analog or digital wired and/or wireless
network that provides information. Such information delivery
networks may support a variety of online services including
Internet and/or web access, e-mail, instant messaging, paging,
chat, interest groups, audio and/or video streaming, and/or
directory services.
[0018] The provider node 110 may receive instructions from a
software application, a program, a piece of code, a device, a
computer, a computer system, or a combination thereof that
independently or collectively directs operations of the node. The
instructions may be embodied permanently or temporarily in any type
of machine, component, equipment, storage medium, or propagated
signal that is capable of being delivered to the provider node
110.
[0019] In one implementation, the provider node 110 includes one or
more informationproviding software applications for accessing and
transmitting requested files to the requestor node 105. The
information-providing applications may run on a general purpose
operating system and a hardware platform that includes a general
purpose processor and/or specialized hardware. Another
implementation may include a reduced operating system with both
general purpose and specialized hardware to operate in mobile
environments.
[0020] One example of an intermediate node 120 is a general-purpose
computer (e.g., a server) capable of responding to and executing
instructions in a defined manner. Other examples include a
workstation, a device, a component, other equipment, or some
combination thereof capable of responding to and executing
instructions. The intermediate node 120 may include and/or form
part of an information delivery network, such as, for example the
Internet, the World Wide Web, an online service provider, and/or
any other analog or digital wired and/or wireless network that
provides information. Such information delivery networks may
support a variety of online services including Internet and/or web
access, e-mail, instant messaging, paging, chat, interest groups,
audio and/or video streaming, and/or directory services.
[0021] The intermediate node 120 may receive instructions from a
software application, a program, a piece of code, a device, a
computer, a computer system, or a combination thereof that
independently or collectively directs operations of the node. The
instructions may be embodied permanently or temporarily in any type
of machine, component, equipment, storage medium, or propagated
signal that is capable of being delivered to the intermediate node
120.
[0022] In one implementation, the intermediate node 120 includes
one or more congestion-reducing software applications for managing
requested files. The congestion-reducing applications may examine
retrieved files and/or file requests to determine whether a
requested file has been stored locally on the intermediate node
120. The congestion-reducing applications may run on a general
purpose operating system and a hardware platform that includes a
general purpose processor and/or specialized hardware. Another
implementation may include a reduced operating system with both
general purpose and specialized hardware to operate in mobile
environments.
[0023] The intermediate node 120 includes an intermediate server
125 connected to and communicating with a cache 130, a digital
signature storage medium 135, and a data compressor 140. While FIG.
1 illustrates each of the cache 130, the digital signature storage
medium 135, the intermediate server 125, and the data compressor
140 as a separate and distinct element within the intermediate node
120, other implementations are possible. Indeed, the functions
associated with an element in the intermediate node 120 may be
performed by any one or more elements of the intermediate node 120
and, in some cases, may be performed by the requester node 105
and/or the provider node 110.
[0024] In one implementation, the intermediate server 125 is
configured to receive a file from a provider node 110 and to
determine the digital signature of the received file. The cache 130
is configured to store files received from the provider node 110.
The cache 130 may store compressed or uncompressed versions of a
file. The intermediate node 120 further includes a digital
signature storage area 135 configured to maintain an index of
digital signatures. The storage area 135 is searchable by the
intermediate server 125 and associates files stored in the cache
130 with entries in the index of digital signatures. The
intermediate server 125 also is connected to a data compressor 140
that is configured to compress files for improved efficiency. The
compressor 140 can include hardware such as a programmed dedicated
processor, or may be implemented as software routines executed on
the general processor(s) of the intermediate server 125.
[0025] The intermediate node 120 may include one or more pieces of
networking infrastructure (e.g., servers, processors, routers,
switches) programmed to maximize network performance. For example,
the intermediate node 120 may include an IP tunnel for converting
data between protocols (e.g., an OSP protocol and standard Internet
protocol) for data transmission between different communications
systems. An IP tunnel also may act as a buffer between requestor
nodes and provider nodes by implementing content filtering and time
saving techniques. In one implementation, the intermediate node 120
is configured to store frequently accessed information in the cache
130 and to provide the stored information to the requestor node 105
locally from the cache 130. In this way, the intermediate node 120
avoids the need to access the Internet in response to a request
from the requestor node 105.
[0026] In another example, the intermediate node 120 includes a web
proxy server configured to look up subscriber information from the
IP address of the requestor node 105 to determine control settings
(e.g., filtering lever) and other demographic information (e.g.,
location, device types) associated with the subscriber. In this
way, the intermediate node 120 can tailor the subscribers content
and user interfaces. Again, the cache 130 may store certain URLs
("Uniform Resource Locators") and other electronic content so that
the intermediate node 120 can locally deliver information to the
requestor node 105.
[0027] The networks 115 connecting the requestor node 105, the
provider node 110, and/or the intermediate node 120 may include one
or more wired and/or wireless communication links. Examples of such
communication links include, but are not limited to, a dial-up
modem connection, a cable modem connection, a DSL line, a WAN
connection, a LAN connection (e.g., Ethernet, Fast Ethernet,
Gigabit Ethernet, Token Ring, ATM), a transceiver connection, a
wireless mobile telephone connection, and/or a satellite link.
[0028] Referring also to FIG. 2, the computer network system 100
operates according to a procedure 200. Initially, the requestor
node 105 requests a file (step 205). In one implementation, the
file request includes a URL identifying a particular provider node
110 and/or data file. The intermediate node 120 receives the file
request from the requester node 105 and then checks whether the
file request can be satisfied by one or more data files stored
locally in the cache 130 (step 210).
[0029] If the requested file is available locally, the local file
is sent (step 215) and received by the requester node (step 220).
In one implementation, numerous identical requests from one or more
requestor nodes 105 cause the intermediate node 120 to locally
store data responsive to the request. Subsequent identical requests
are satisfied using the data residing on the intermediate node 120
without contacting the provider node 110. For example, content
residing at a frequently requested URL may be stored in the cache
222 of the intermediate node 120 when the number of requests for
the popular URL exceeds a threshold value. Once the responsive data
is stored locally, the intermediate node 120 can retrieve the
requested content and transmit that content to the requestor node
105 without having to access the servers residing at the URL. This
greatly reduces delay experienced by the requestor node 105.
[0030] If the request from the requestor node cannot be satisfied
locally, the intermediate node 110 transmits the file request to
the provider node 110 (step 225). Upon receiving the file request
(step 230), the provider node 110 identifies and retrieves the data
file responsive to the request. The retrieved file may include any
type of data including, but not limited to, text data, image data,
audio data, video data, HTML or other markup language, and/or data
associated with an Internet site, Web page, electronic message or
attachment. The provider node 110 then sends the requested file to
the intermediate node 120 (step 235). The intermediate node 120
receives the retrieved file from the provider node 110 (step 240)
and determines a digital signature for the retrieved file (step
245).
[0031] Determining the signature may be accomplished in different
ways. For example, the intermediate node 120 may determine the
digital signature by applying a hashing technique to at least a
portion of the requested data file. The output of the hashing
techniques is referred to as a hash value. The hash value is
substantially smaller than the requested digital file, and is
generated from an algorithm in such a way that it is extremely
unlikely that different data files will produce the same hash
value. One example of a hashing technique is a proprietary hashing
algorithm used by an OSP. Other examples of hashing techniques
include, but are not limited to, the MD5 family of algorithms
and/or the SHA family of algorithms.
[0032] Referring now to FIG. 3, the intermediate node 110 also may
determine the digital signature by decrypting an encrypted digital
signature received from the provider node 110. In one
implementation, the provider node 110 receives a file request (step
305), retrieves the requested file (step 310), and then applies a
hashing technique to the requested data file. Next, the data file
and the obtained hash value are encrypted (step 320) and then sent
to the intermediate node 105 (step 325). Upon receiving the
encrypted data from the provider node 110 (step 330), the
intermediate node 120 decrypts the data file and the hash value
using an appropriate key (step 335). In order to verify the
integrity of the data file, the intermediate node 120 may perform
the same hashing technique applied by the provider node 110 (step
340) and compare the resulting hash value to the decrypted hash
value (step 345). If the hash vales are the same, the integrity of
the data was preserved across the network 115 and the hash value
may be used as the digital signature (step 350).
[0033] In another implementation, the provider node 110 transmits a
batch of frequently requested files to the intermediate node 120
for local storage along with corresponding digital signatures for
each file. The provider node 110 may send the frequently requested
files proactively or may send a dynamic reference (e.g., link) for
accessing a version of the file stored closer to the intermediate
node.
[0034] Referring to FIG. 4, in yet another implementation, the
provider node 110 receives a file request (step 405), retrieves the
requested file (step 410), and creates a digital signature for the
requested file (step 415). Next, the provider node 110 sends only
the digital signature for the requested file to the intermediate
node 120 (step 420). The intermediate node 130 receives the digital
signature of the requested file (step 425) and then uses the
transmitted signature to determine whether the file is already
stored in the cache 130 (step 430). Typically, the file will be
referenced under a different name such that the intermediate node
120 did not previously identify the file as being available
locally. The intermediate node 120 requests the actual file only if
the signature is not included in the index of signatures.
[0035] Referring again to FIG. 2, once the digital signature is
determined (step 245), the intermediate node 120 looks up the
digital signature in an index of signatures (step 250). In one
implementation, the index of signatures is stored within the
intermediate node 120 in a digital signature storage area 135. The
index of signatures, however, may be stored in a separate hardware
device. The digital signature storage area 135 may include any type
of device and/or storage medium (e.g., memory, disc, propagated
signal) having volatile or nonvolatile storage capacity.
[0036] The index of signatures is associated with
previously-compressed files stored in the intermediate node 120. In
one implementation, the index includes a comprehensive list of all
compressed files stored in the cache 130 of the intermediate node
120. The index of signatures may include pointers (e.g., links) to
the compressed files stored in the cache 130. The digital
signatures may be listed or ranked by popularity, numerically,
historically, or in any other way that facilitates searching. The
index of signatures may be compiled by the intermediate node, as
discussed in more detail below, and/or imported from neighboring
devices, such as, for example, other intermediate nodes 120 and/or
provider nodes 110. An imported index of signatures may be merged
with an existing index of signatures to form a composite index of
signatures. Duplicate entries may be eliminated from the composite
index of signatures.
[0037] If the digital signature is not found in the index of
signatures, the intermediate node 120 may compress the requested
file (step 255), store the compressed file in the cache 130 (step
260), and then add the digital signature in the index of signatures
135 (step 265).
[0038] Compressing the retrieved file may be accomplished in a
variety of ways and may include decompressing precompressed files
(such as .JPEG, and .TIF) and recompressing the files into more
efficient formats. The compressed versions of frequently requested
files may be stored in the cache 130 to provide faster response to
a requestor node 105. Any caching algorithm may be used, such as a
conventional "least recently used" (LRU) algorithm, to manage file
storage in the cache 130. The intermediate node 120 may maintain a
log of file requests and select files to be cached based upon
logged request frequencies. Caching may be done on-line, while
compressing files, or off-line using logged request frequencies to
retrieve popular files and compress the files during idle time for
the intermediate node 120.
[0039] In some cases, it may be advantageous to store more than one
copy of a compressed file on the intermediate node 110. For
example, a number of copies according to a predetermined ratio of
stored copies to users may be stored to accomplish load balancing.
In one implementation, the intermediate node 120 includes a counter
(not shown) to keep track of the number of times a file is
retrieved. At high frequencies, the intermediate node 120 may store
multiple instances of the compressed file to handle the volume of
requests. When the frequency diminishes, instances of the file may
be removed.
[0040] Some implementations may better manage high demand
conditions by storing multiple instances of the index of digital
signatures 135, and/or including multiple intermediate nodes 120.
In high demand conditions, the multiple stored files, multiple
indexes of digital signatures 135, and/or multiple intermediate
nodes 120 are allocated (e.g., round robin assigned) to users. For
example, when multiple versions of a compressed file are stored,
the intermediate node 120 will alternate among which instance is
transmitted.
[0041] Other implementations may initially add a digital signature
to the index of signatures 135 but will only store the compressed
version of the retrieved file if the digital signature is found in
the index of signatures a threshold number of times. For example,
the intermediate node 120 may store a retrieved web file only when
the retrieved web file has been requested at least five hundred
times in a one hour period.
[0042] Another implementation may include keeping a time stamp with
the digital signature. For example, when a digital signature is
added to the index of signatures 135, the time stamp will indicate
when the digital signature was added. The time stamp may be used to
keep the index of signatures 135 current, and subsequent matches to
the digital signature may update the time stamp. The time stamp
also may be used to remove digital signatures corresponding to
files that have not been frequently and/or recently requested.
[0043] If the digital signature is found in the index of signatures
135, a compressed version of the file is retrieved, transmitted to
the requestor node 105 (step 270), and finally received by the
requester node 105 (step 275). In one implementation, shown in FIG.
5, the intermediate server 125 determines the digital signature of
a requested file (step 505) and determining whether the digital
signature exists in the index of signatures 135 (step 510). If the
digital signature exists in the index, the intermediate node 120
locates the compressed file associated with the digital signature
that is stored in the cache 130 (step 515). The digital signature
in the index may be linked and/or otherwise referred to the
associated compressed file. The intermediate server 125 retrieves
the compressed file from the cache 130 (step 520) and forwards the
compressed file to the requestor node 105 (step 530). The requestor
node 105 receives the compressed file (step 535) and then delivers
the compressed version or an uncompressed version to the user.
[0044] To ensure that a retrieved file corresponds to the digital
signature, the intermediate node 120 may verify the content of the
retrieved compressed file (step 525). In one implementation, this
step is performed prior to forwarding the compressed file to the
requestor node 105. Examples of verifying content include, but are
not limited to, examining and/or comparing a name, size, hash
value, and/or data associated with the retrieved file.
[0045] Additional processing also may be done to ensure time
savings. For example, if a requested file is small, the time
required to perform the sequence of steps including determining the
signature for the file may exceed the time required to transfer the
file directly. In general, if T.sub.t is the estimated transfer
time for a file and Td is the time to perform the sequence of
steps, then the intermediate node methods should only be used where
T.sub.d<T.sub.t. Estimates for T.sub.t can be readily obtained
by measuring the actual bit rate to a particular requestor node, in
known fashion. Estimates for T.sub.d can be generated by first
performing, in a preparation stage, a statistical analysis of
actual signature determination times for a file size; as well as
the time to generate the digital signature and compress a requested
file. Thus, by knowing the size of a particular requested file, an
estimate can be readily determined for T.sub.t and T.sub.d by
extrapolation. Alternatively, an estimate for T.sub.d can be
generated by performing the sequence of steps on a portion of a
file, timing each action, and extrapolating to the entire file
size.
[0046] The intermediate node methods, devices and programs may be
implemented in hardware or software, or a combination of both. In
some implementations, the intermediate node methods, devices and
programs are implemented in computer programs executing on
programmable computers each with at least one processor, a data
storage system (including volatile and non-volatile memory and/or
storage elements), at least one input device, and at least one
output device. Program code is applied to input data to perform the
functions described herein and generate output information. The
output information is applied to one or more output devices.
[0047] The intermediate node methods, devices and programs may be
implemented as a computer program storable on a medium that can be
read by a computer system, such as an intermediate server 125,
configured to provide the functions described herein. Again, while
the intermediate node methods, devices and programs have been
described as if executed on a separate processor, the intermediate
node methods, devices and programs may be implemented as a software
process executed within one or more intermediate servers 125.
[0048] Each program is preferably implemented in a high level
procedural or object oriented programming language to communicate
with a computer system. However, the programs can be implemented in
assembly or machine language, if desired. In any case, the language
may be a compiled or interpreted language.
[0049] Each such computer program is preferably stored on a storage
media or device (e.g., ROM or magnetic diskette) readable by a
general or special purpose programmable computer, for configuring
and operating the computer when the storage media or device is read
by the computer to perform the procedures described herein. The
computer readable medium can also be a propagated signal. The
intermediate node 220 system may also be considered to be
implemented as a computer-readable storage medium, configured with
a computer program, where the storage medium so configured causes a
computer to operate in a specific and predefined manner to perform
the functions described herein.
[0050] A number of implementations have been described.
Nevertheless, it will be understood that various modifications may
be made. For example, although the intermediate node methods,
devices and programs have been described in the context of a wide
area public network, the intermediate node methods, devices and
programs can be applied to any network (including private wide area
and local area networks) in which files requested from one node by
another node pass through an intermediate processor that can be
programmed or configured as an intermediate node 120.
[0051] Other implementations are within the scope of the following
claims.
* * * * *